Electronic devices such as mobile phones, laptop computers, electronic notebooks, digital cameras, and video game instruments have an audio function. Such an electronic device having an audio function includes a housing, inside which is placed a sound emitting part such as a speaker or buzzer or a sound receiving part such as a microphone. The housing is typically provided with an opening for directing sound to the sound emitting part or the sound receiving part.
It is common practice to cover the opening of the housing by a waterproof sound-permeable membrane in order to prevent foreign matters such as water drops from entering the housing of the electronic device. Known examples of the waterproof sound-permeable membrane include porous polytetrafluoroethylene (PTFE) membranes (see Patent Literature 1 to 3). A porous polytetrafluoroethylene membrane used as a waterproof sound-permeable membrane is produced by stretching a shaped product containing a fine polytetrafluoroethylene powder and a liquid lubricant so as to form pores in the shaped product.